By Laura Forman

Wednesday's antitrust hearing before Congress made tech giants like Google-parent Alphabet, Inc. and Facebook seem like they've rigged the deck. But Thursday's second quarter reports from both companies made the ad game look a little more fair.

Google may be a search monopoly, but its exposure to hard-hit sectors like travel seems to be hurting it at the moment. The company reported the first on-year decline in advertising revenue in its history. Meanwhile Facebook said its own ad growth slowed to 10% from a year earlier in the quarter. That's down from 17% growth in the first quarter and significantly lower than its quarterly average of nearly 30% over the previous two years. But Facebook's double-digit growth was still well above Wall Street's tempered expectations, sending shares up 6% in after-hours trading on Thursday. Google shares were little changed.

Facebook said it saw second quarter resilience due to strength from small businesses leveraging direct response ads, as well as businesses transitioning online to Facebook Shops amid the pandemic. The company said it saw a considerable ad recovery in May and June with advertisers on its platform now totaling nine million, up from eight million reported last quarter.

Facebook's shares were also boosted by a better-than-expected outlook for its ad business in the third quarter, basically saying it should be in line with the second quarter. That is even after accounting for pressure from macroeconomic uncertainty, the continuing ad boycott and regulatory headwinds. The implied 10% quarterly growth rate would be well above the Street's expectation of 6.7%.

For its part, Google's ad business seems more vulnerable to current events. "Search and other" advertising revenues fell 10% year-over-year, according to the company, but finished essentially flat by the end of June. On a conference call for investors, Chief Financial Officer Ruth Porat said that advertising revenue improved throughout the quarter, and that search ad revenue had even modestly improved throughout July. Investors shouldn't put too much hope in that recovery, though: Ms. Porat warned that it would be "premature to gauge the durability of recent trends," given the fragile macroenvironment.

Indeed, Google's top line may be vulnerable to search verticals particularly at risk. Bernstein analyst Mark Shmulik estimates travel and auto contribute 15% to 20% of Google's search revenue. Travel has been especially slow to recover. Earlier this week, global hotel search platform Trivago cited renewed weakness in its U.S. business in mid-June and said it expects international travel to be limited for the foreseeable future. Meanwhile the International Transport Association is now predicting global passenger traffic won't return to pre-Covid levels until 2024.

On its call, Google reiterated that global macroeconomic performance has tended to be correlated with ad spending, calling it "a key signal to monitor." In that context, Thursday's report from the Commerce Department, which showed the U.S. economy registering its worst contraction on record, certainly doesn't portend a winning next hand.

At least one tech titan seems hostage to events outside its control.

Write to Laura Forman at laura.forman@wsj.com